The present invention relates generally to an industrial gas fired catalytic radiant burner for drying or heating an article or substance, and more particularly to an economical burner which has high radiant efficiency at a wide range of firing rates with low emissions.
Industrial burners are used to dry and cure products coated with paint, primers and other polymeric coatings; dry food or grain; perform plastic thermoforming; create steam; heat water; dry paper, ink or other liquid films; perform glass annealing, and other things. In addition, burners have many other potential applications including use for power generation in gas turbines and use as a short contact time, high temperature incinerator for pollutant containing air streams.
In radiant burners, oxygen from the air oxidizes a gas when a mixture of air and gas reaches a certain temperature. The mixture is heated by passing the mixture through openings of a heated substrate, which causes the oxidation of the gas and ideally produces only carbon dioxide, water and heat. Some of the heat released from the oxidation process is then used to heat the substrate for oxidation of more gas.
When oxidation is incomplete, unwanted high emissions and unburned hydrocarbons are produced. A known reticulated homogeneous burner operating with a composition of 10% excess air and a firing rate of 100 kBTU/hr ft.sup.2 was found to release relatively high emissions of 40 ppm of unburned hydrocarbons, 50 ppm carbon monoxide and 12 ppm nitrogen oxides.
Some heterogeneous gas burners are designed to lower the emissions and raise the efficiency of the burner with the use of a catalyst layer that includes a certain chemical coating or catalyst placed on a heated surface or support. Most of these catalytic combustors operate at cool temperatures (&lt;500.degree. C.) which limits the surface reaction rates or mass transfer in the pores of the support. At high operating temperatures (up to 1500.degree. C.), current catalytic burners have high emissions and fall substantially short of the possible 38% efficiency using a simple energy balance because high surface temperatures associated with ignition causes dispersed catalyst and support particles to sinter and block the pores, which causes catalyst deactivation. These catalytic burners have catalyst layers with relatively large total specific surface areas (e.g. including wash coats).
In addition, nobel metal platinum has been used as the catalyst because of its thermal properties, but platinum can be very expensive when large amounts of the platinum are required for efficient heating. Finally, high radiant efficiency is difficult to maintain at high temperatures because of the large amount of oxygen required for complete oxidation.
Accordingly, it is an object of the present invention to provide an improved catalytic radiant burner with a high radiant efficiency and low emissions operating at a wide range of temperatures.
More specifically, an object of the present invention is to provide an improved burner such that efficiency approaches the predicted 38% calculated from a simple energy balance using a one point radiation efficiency measurement, while assuming that the surface and gas phase temperatures are equal.
An additional object of the present invention is to provide an improved burner that converts 99.9% of the hydrocarbons in the gas and produces very low emissions of nitrogen oxides and carbon monoxide.
A further object of the present invention is to provide a catalyst with a more efficient support and a more economical amount of coating while still maintaining a wide range of temperatures (or a high turndown ratio) including very high operating temperatures.
Yet an additional object of the present invention is to provide large amounts of oxygen at a high rate in order to maintain high temperatures.
These and other objects of the present invention are discussed or will be apparent from the detailed description of the invention.